6,327 research outputs found
Symplectic Geometry on Quantum Plane
A study of symplectic forms associated with two dimensional quantum planes
and the quantum sphere in a three dimensional orthogonal quantum plane is
provided. The associated Hamiltonian vector fields and Poissonian algebraic
relations are made explicit.Comment: 12 pages, Late
A unified lattice Boltzmann model and application to multiphase flows
In this work, we develop a unified lattice Boltzmann model (ULBM) framework that can seamlessly integrate the widely used lattice Boltzmann collision operators, including the Bhatnagar–Gross–Krook or single-relation-time, multiple-relaxation-time, central-moment or cascaded lattice Boltzmann method and multiple entropic operators (KBC). Such a framework clarifies the relations among the existing collision operators and greatly facilitates model comparison and development as well as coding. Importantly, any LB model or treatment constructed for a specific collision operator could be easily adopted by other operators. We demonstrate the flexibility and power of the ULBM framework through three multiphase flow problems: the rheology of an emulsion, splashing of a droplet on a liquid film and dynamics of pool boiling. Further exploration of ULBM for a wide variety of phenomena would be both realistic and beneficial, making the LBM more accessible to non-specialists.
This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’
Lattice Boltzmann simulation of a water droplet penetrating a micropillar array in a microchannel
Water droplets penetrating a microchannel equipped with an array of micropillars are commonly seen in engineering applications, ranging from micro-electro-mechanical systems to macro-heat-transfer facilities. Understanding the detailed droplet dynamics in this process is therefore beneficial to the advancement of many fields of industry. In this study, we adopt a nonorthogonal multiple-relaxation-time lattice Boltzmann model to simulate a water droplet penetrating a micropillar array in a microchannel. We first validate our model against the experimental results of (a) off-center impact of a water droplet on a ridged superhydrophobic surface and (b) impact of a water droplet on a curved superhydrophobic surface. Then a comprehensive parametric study is carried out by changing the droplet initial velocity, opening fraction of the micropillar array, and wettability of the micropillar surface. It is found that when the droplet penetrates the micropillar array, its fingering dynamics in the longitudinal direction is governed by the competition between the dynamic and capillary pressures, while the permeation process in the lateral and vertical directions is dominated by the capillary effect. The change of the droplet initial velocity and configuration setup can significantly influence the droplet penetration velocity, maximum wetted surface area, and penetration rate. Finally, a theoretical model is proposed to describe the transient evolution of the droplet penetration mass for a variety of Weber numbers, opening fractions, and static contact angles
A framework for evaluating automatic image annotation algorithms
Several Automatic Image Annotation (AIA) algorithms have been introduced recently, which have been found to outperform previous models. However, each one of them has been evaluated using either different descriptors, collections or parts of collections, or "easy" settings. This fact renders their results non-comparable, while we show that collection-specific properties are responsible for the high reported performance measures, and not the actual models. In this paper we introduce a framework for the evaluation of image annotation models, which we use to evaluate two state-of-the-art AIA algorithms. Our findings reveal that a simple Support Vector Machine (SVM) approach using Global MPEG-7 Features outperforms state-of-the-art AIA models across several collection settings. It seems that these models heavily depend on the set of features and the data used, while it is easy to exploit collection-specific properties, such as tag popularity especially in the commonly used Corel 5K dataset and still achieve good performance
Fluctuation-Driven Vortex Fractionalization in Topologically Ordered Superfluids of Cold Atoms
We have studied spin structures of fluctuation-driven fractionalized vortices
and topological spin order in 2D nematic superfluids of cold sodium atoms. Our
Monte Carlo simulations suggest a softened pi-spin disclination structure in a
half-quantum vortex when spin correlations are short ranged; in addition,
calculations indicate that a unique non-local topological spin order emerges
simultaneously as cold atoms become a superfluid below a critical temperature.
We have also estimated fluctuation-dependent critical frequencies for
half-quantum vortex nucleation in rotating optical traps and discussed probing
these excitations in experiments.Comment: 5 pages, 2 figures; revised version accepted by Europhysics Letter
Quantitative Assessment of Robotic Swarm Coverage
This paper studies a generally applicable, sensitive, and intuitive error
metric for the assessment of robotic swarm density controller performance.
Inspired by vortex blob numerical methods, it overcomes the shortcomings of a
common strategy based on discretization, and unifies other continuous notions
of coverage. We present two benchmarks against which to compare the error
metric value of a given swarm configuration: non-trivial bounds on the error
metric, and the probability density function of the error metric when robot
positions are sampled at random from the target swarm distribution. We give
rigorous results that this probability density function of the error metric
obeys a central limit theorem, allowing for more efficient numerical
approximation. For both of these benchmarks, we present supporting theory,
computation methodology, examples, and MATLAB implementation code.Comment: Proceedings of the 15th International Conference on Informatics in
Control, Automation and Robotics (ICINCO), Porto, Portugal, 29--31 July 2018.
11 pages, 4 figure
Integration and Communication of Process Support Tools in an Online Virtual Learning Environment
The Education through Virtual Experience (EVE) research group based at the National University of Ireland Maynooth have successfully developed an online Virtual Learning Environment (VLE) for Astronomy as part of the Virtual Telescopes in Education (VTIE) project. The VTIE VLE has been developed to provide online software support for the engagement of schoolchildren and their teachers in a scientific process. The development of an online VLE to support a scientific process has brought about complex interactions from the user perspective. This has lead to complex integration and communication challenges from the software implementation perspective. This paper contains a high level user-centered summary of the integration and communication challenges that have arisen during the VLE development and summarizes the mechanisms used to meet these challenges
Berry's Phases of Ground States of Interacting Spin-One Bosons: Chains of Monopoles and Monosegments
We study Berry's connection potentials of many-body ground states of spin-one
bosons with antiferromagnetic interactions in adiabatically varying magnetic
fields. We find that Berry's connection potentials are generally determined by,
instead of usual singular monopoles, linearly positioned monosegments each of
which carries one unit of topological charge; in the absence of a magnetic
field gradient this distribution of monosegments becomes a linear chain of
monopoles. Consequently, Berry's phases consist of a series of step functions
of magnetic fields; a magnetic field gradient causes rounding of these
step-functions. We also calculate Berry's connection fields, profiles of
monosegments and show that the total topological charge is conserved in a
parameter space
Composition dependence of electronic structure and optical properties of Hf1-xSixOy gate dielectrics
Copyright © 2008 American Institute of Physics. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditionsComposition-dependent electronic structure and optical properties of Hf1−xSixOy 0.1 x 0.6 gate
dielectrics on Si at 450 °C grown by UV-photo-induced chemical vapor deposition UV-CVD have
been investigated via x-ray photoemission spectroscopy and spectroscopy ellipsometry SE . By
means of the chemical shifts in the Hf 4f, Si 2p, and O 1s spectra, the Hf–O–Si bondings in the
as-deposited films have been confirmed. Analyses of composition-dependent band alignment of
Hf1−xSixOy / Si gate stacks have shown that the valence band VB offset Ev demonstrates little
change; however, the values of conduction band offset Ec increase with the increase in the silicon
atomic composition, resulting from the increase in the separation between oxygen 2p orbital VB
state and antibonding d states intermixed of Hf and Si. Analysis by SE, based on the Tauc–Lorentz
model, has indicated that decreases in the optical dielectric constant and increase in band gap have
been observed as a function of silicon contents. Changes in the complex dielectric functions and
band gap Eg related to the silicon concentration in the films are discussed systematically. From the
band offset and band gap viewpoint, these results suggest that Hf1−xSixOy films provide sufficient
tunneling barriers for electrons and holes, making them promising candidates as alternative gate
dielectrics.National Natural Science Foundation of China and Royal Society U.K
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